The above-identified patent concerns the problem of activating more than one yarn-carrying finger at a striping box of a cirular knitting machine and keeping such plural fingers activated for integral numbers of needle-cylinder rotations when the selection of yarn-carrying fingers is performed using an indexed control drum having axial slots which receive L-shaped finger-activating jacks. That patent discloses several ways of activating different combinations of fingers. For the case where the control drum is provided with a holding spring midway between its ends, for holding down and properly positioning the axial legs of such L-shaped jacks, problems arise when simultaneously activating yarn-carrying fingers located to opposite axial sides of the holding spring. Typically, the holding spring is so strong and tight that an attempt to insert beneath it a jack having two radial legs which are to be located to either side of the holding spring, e.g., to activate the middle two of four yarn-carrying fingers of the striping box, is exceedingly difficult when not simply impossible; striping boxes of this type are designed for activating one yarn-carrying finger at a time, and do not naturally lend themselves to activation of frequently changing combinations of e.g., two fingers at a time, the two fingers being located, at least sometimes, at axially opposite sides of the holding spring.